This invention is directed generally to improvements in television receivers, and particularly to a vertical ramp generator for use in such a receiver.
Television receivers typically include a cathode ray tube which scans both vertically and horizontally to develop an interlaced raster. Vertical scan is usually effected by applying a vertical drive signal to a yoke which is coupled to the neck of the picture tube.
To develop the vertical drive signal, a ramp generator may be employed whose function is to charge and discharge a capacitor so as to develop a ramp voltage across the capacitor. The latter voltage may be processed and applied to the yoke for effecting trace and retrace of the receiver's vertical scan.
Among the factors to be considered in developing the ramp voltage is the peak current required to charge the capacitor, the linearity of the ramp, and its freedom from undesired components which impair interlace. Prior ramp generators have generally presented difficulties on one or more of these areas. For example, some ramp generators have required high peak charging currents which place an undesirably high load on the receiver's power supply. Others have generated ramp voltages which include horizontal and vertical rate components which make good interlace very difficult to achieve. The present invention overcomes these problems with a ramp generator which is particularly adapted for construction in integrated circuit form.